<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>form_select_optgroup</title>
</head>
<body>

    <h1>通过标签把相关的选项组合在一起</h1>

    <select>
        <optgroup label="a" va>
            <option value="a1">A1</option>
            <option value="a2" selected="selected">A2</option>
            <option value="a3">A3</option>
        </optgroup>

        <optgroup label="b">
            <option value="b1">B1</option>
            <option value="b2">B2</option>
        </optgroup>

        <option value="c">C</option>
    </select>
    <br>

</body>
</html>